1. Field of the Invention
This invention relates to an in-line filter. More particularly, it relates to an in-line filter which can be used with standard types of tubing connectors designed for tubing carrying gases used in the manufacture of semiconductors.
2. Description of the Related Art
Various gases are employed in the manufacture of semiconductors. Because particulate matter in the gases can introduce flaws into the semiconductors being manufactured, it is important that the gases be of extremely high cleanliness. Therefore, it is common to install in-line particulate filters along tubing lines for carrying these gases. An in-line filter refers to a filter which has a straight-line flow path (the inlet, the filter element, and the outlet of the filter being substantially coaxial) and which is easily installed in a tubing line.
A conventional in-line filter for use with tubing lines includes a metallic housing having a tubular body with threaded connections at opposite ends and a filter element welded to the inside of the housing. In use, the housing is placed between two sections of tubing which are to be joined, each section of tubing having one half of a standard tubing connector installed on its end. The threaded connections of the housing are then sealingly connected to the two halves of the tubing connector to form a threaded joint.
An in-line filter of this type has a number of drawbacks. One is that it increases the length of the tubing line by the length of the housing, so in some cases, it is difficult or impossible to retrofit an existing tubing line with such a filter. Furthermore, because a connection is formed at each end of the housing, the number of connections in the tubing line is greater than in the absence of the in-line filter, so the number of possible sources of contamination or leakage increases. In addition, since the filter element is welded inside the housing, it is impossible to inspect the filter element without damaging the housing or the filter element.